1. Field of the Invention
The invention is related to the field of reaming tools used to enlarge the diameter of wellbores drilled through the earth beyond the diameter of a drill bit used to initially drill the wellbore through earth.
2. Description of the Related Art
Drill bits used to drill wellbores through earth formations typically have a nominal diameter, that is, a diameter of a borehole that will be created when the drill bit is rotated and impressed axially onto the formations. Frequently it is desirable to enlarge the diameter of the borehole beyond the nominal diameter of the drill bit. Specialized drill bits, known as bi-center bits, have been developed to create boreholes having drilled diameters greater than the diameter of an opening through which such bits will pass when they are not rotated. Other tools for enlarging a borehole beyond the nominal diameter of a symmetric bit (one whose drill diameter is substantially the same as its nominal diameter) include reamer wings. Reamer wings are typically assembled to a drilling tool assembly (drill string) at a selected axial position behind (away from the drilling surface) the drill bit. Reamer wings have cutting elements positioned on blades which extend radially outward from the rotational center of the drill string to a greater distance therefrom than the radius of the drill bit. When the reamer wing is rotated, the cutting elements drill the enlarged borehole.
Reamer wings are described for example in U.S. Pat. No. 5,495,899 issued to Pastusek et al, U.S. Pat. No. 5,497,842 issued to Pastusek et al, and U.S. Pat. No. 5,765,653 issued to Doster et al. Reamer wings typically include a tubular housing or body having a number of longitudinally extensive, azimuthally spaced apart, and generally radially-extending blades. The blades having cutting elements on them. The cutting elements are typically polycrystalline diamond compact inserts, carbide inserts or a combination of these. The reamer wings known in the art are susceptible to drilling a borehole in which the surface of the borehole is not smooth and round. Further, the reaming wings known in the art are susceptible to damage to the cutting elements affixed to the blades. Still further, the reamer wings known in the art are typically unable to drill out equipment used to cement a steel a casing in place in the borehole (float equipment) without damage to the cutting elements on the blades.
One aspect of the invention is a reaming tool including a body having reaming blades affixed to the body at azimuthally spaced apart locations. The reaming blades have cutters attached to them at selected positions. An outermost surface of each one of the reaming blades conforms to a radially least extensive one, with respect to the longitudinal axis of the reaming tool, of a pass through circle and a drill circle. The drill circle is substantially coaxial with the longitudinal axis. The pass-through circle is axially offset from the drill circle and defines an arcuate section inside which the pass-through circle extends from the longitudinal axis beyond the lateral extent of the drill circle, so that radially outermost cutters disposed on the reaming blades positioned azimuthally within the arcuate section will drill a hole having a drill diameter substantially twice a maximum lateral extension of the reaming blades from the longitudinal axis, while substantially avoiding wall contact along an opening having a diameter of the pass through circle. In one embodiment of this aspect of the invention, the reaming blades positioned azimuthally outside the arcuate section include wear resistant inserts on their outermost surfaces. In one example, the inserts are tungsten carbide, polycrystalline diamond or the like.
Another aspect of the invention is a reaming tool including a body having reaming blades affixed to them at azimuthally spaced apart locations. The reaming blades have cutters attached to them at selected positions along each one of the reaming blades. In this aspect of the invention, the reaming tool includes a pilot hole conditioning section having a plurality of azimuthally spaced apart blades (xe2x80x9cPilot bladesxe2x80x9d) affixed to the body longitudinally ahead of the reaming blades. The pilot blades include a taper on their downhole ends, a gauge pad having a diameter substantially equal to a drill diameter of a pilot bit used to drill a pilot hole longitudinally ahead of the reaming tool, and an intermediate cutter affixed to selected ones of the pilot blades longitudinally behind the gauge pad. The intermediate cutters are positioned laterally so as to drill a hole having an intermediate diameter larger than the pilot hole diameter and smaller than a drill diameter of the reaming tool. The pilot blades include an intermediate gauge pad axially xe2x80x9cupholexe2x80x9d of the intermediate cutters, if used, these gauge pads having a diameter substantially equal to the intermediate diameter.
Another aspect of the invention is a reaming tool including a body having reaming blades affixed to the body at azimuthally spaced apart locations around the circumference of the body. The reaming blades each have at least one cutter attached to them at a selected position along each of the blades, the position and/or orientation of the cutter selected to minimize lateral force imbalance of the reaming tool. One embodiment of this aspect of the invention includes a pilot hole conditioning section having a plurality of azimuthally spaced apart pilot blades affixed to the reaming tool body longitudinally ahead of the reaming blades.
Another aspect of the invention is a reaming tool including a body having reaming blades affixed to the body at azimuthally spaced apart locations around a circumference of the body. Selected ones of the reaming blades include cutters attached to them at selected positions. In this aspect of the invention, the reamer includes a pilot hole conditioning section, including a plurality of azimuthally spaced apart pilot blades affixed to the reamer body longitudinally ahead of the reaming blades. At least one of the reaming blades is formed as a single structure with an azimuthally corresponding one of the pilot blades.
Another aspect of the invention is a reaming tool including a plurality of reaming blades affixed to a body at azimuthally spaced apart locations. Selected ones of the reaming blades are formed as spirals.
Another aspect of the invention is a reaming tool including a body having reaming blades affixed to the body at azimuthally spaced apart locations around a circumference of the body. Selected ones of the reaming blades include cutters on them at selected positions. The reaming tool in this aspect also includes a pilot hole conditioning section having a plurality of azimuthally spaced apart pilot blades affixed to the body longitudinally ahead of the reaming blades. The pilot blades each include a taper on the downhole end of the blade, a gauge pad having a diameter substantially equal to a drill diameter of a pilot bit used to drill a pilot hole longitudinally ahead of the reaming tool, and at least one intermediate cutter affixed to selected ones of the pilot blades longitudinally behind the gauge pad. The at least one intermediate cutter is laterally positioned to drill a hole having an intermediate diameter larger than the pilot hole and smaller than a drill diameter of the reaming tool. Selected ones of the pilot blades include an intermediate gauge pad having a diameter substantially equal to the intermediate diameter. At least one of a position and an orientation of the at least one intermediate cutter is selected so that net lateral force generated by the reaming tool is within about twenty percent of the axial force (weight on bit) applied to the reaming tool. In another embodiment, the net lateral force is within about 15 percent of the axial force on the reaming tool (weight on bit). In a particular embodiment of this aspect of the invention, the pilot blades include a taper on the downhole edge. Selected ones of the tapers can include an auxiliary cutter thereon.